Eli Shahar's entry in the 12.08.18 Digest regarding the Ampico "A"
expression cut-out unit implies that unit is controlled by the
"pneumatic with a finger bar."

This is incorrect.  He is referring to the "cancel" pneumatic which
opens when the Ampico switch is "Off", which, in turn, continuously
enables both bass and treble cancel valves of the expression units,
thereby ensuring that any perforations of a non-Ampico roll being
played that occur in any of the expression tracks (chiefly 2-4-6B
and 2-4-6T) do not spuriously "set" any of those intensities, with
no way to cancel them.

The cut-out unit itself is instead controlled (turned on or off) by
the position of the Ampico switch.  If it is "on", the unit passes
all expression signals to their respective valves.  If it is "off", it
inhibits all of these same signals EXCEPT 3B, the sustain pedal.  This
allows "normal" sustain perfs to still operate the sustain pedal.

(This brings up another question: Why did the Ampico "engineers"
see fit to include a separate turn switch (Pedal) that inhibits or
allows the sustain pneumatic to respond to sustain perfs?  Perhaps
it's a hold-over from typical early player piano designs that included
this defeat feature.  Personally, I have never heard a piano roll,
expression or otherwise, where sustain perfs are present, that sounded
better with the sustain inhibited.)

(Curiously, these (apparently) same engineers did _not_ have the Ampico
re-wind track (8T) pass through the expression cut-out unit.  Therefore,
a non-expression roll that plays the high A# note will trigger a
spurious re-wind, even when the Ampico switch is "off".)

Bruce Clark (in the same MMD issue) suggests some other causes but it
would be helpful if the Tom Gregory could give us a few more details
about how his Ampico is performing.  Specifically, does a typical roll
start off okay then the treble gets too loud and does not get softer?

In that case, the treble cancel valve _may_ not be operating correctly,
or one or more of the intensity valves (2-4-6) is not resetting when
the cancel valve tells it to.  If there is a step-offset between the
bass and treble loudness from the very start of the roll, then it
sounds like more leakage in the bass side of the stack than the treble,
which can have multiple causes.  Or, the bass cancel valve may be
sprung continuously, either because of a defect in the valve or leakage
in the cut-out unit, which prevents any bass intensities from being
set, or one or more of the bass intensities are not setting in the
first place, or ... ...

If Tom plays only Ampico rolls, eliminating the cut-out unit is okay,
but I'm betting the problem is elsewhere.

John Grant